This invention relates to a cell structure for an electrochemical cell.
An electrochemical cell may be used to electrolytically separate water into its components, hydrogen and oxygen or, alternatively, combine hydrogen with oxygen to generate electricity. Each electrochemical cell typically has an anode cavity, a cathode cavity and an electrolyte. The electrolyte may be an ionically conductive material, such as an ion-exchange membrane or liquid contained in a porous matrix. The electrolyte is positioned between the anode cavity and the cathode cavity and serves to control the exchange of electrical charge and fluid between the two cavities.
FIG. 1 illustrates an exploded view of an electrochemical cell 12 known in the art. As shown, electrochemical cell 12 has anode cavity 10 and cathode cavity 14 arranged between separator plates 32. Each cavity 10, 14 comprises a series of electrically conductive round metal plates 18, which are stacked upon one another to form a cylinder. Each plate 18 may have a central area or active area 22 comprising a mesh screen filled with openings that permit the passage of fluid through each plate 18. A peripheral area or a seal area 24 surrounds the mesh screen to form a seal that prevents the leakage of fluid out of the active area 22. When all of the active areas 22, 23 of each the plates 18 are aligned, the stack of mesh screens form a fluid cavity, both an anode cavity and a cathode cavity.
Anode cavity 10 is spaced from cathode cavity 14. Together, these cavities 10, 14 sandwich electrochemically conductive medium 28, here an ion-exchange membrane. It is through this membrane that fluid and charge are communicated for either the separation of hydrogen and oxygen or their combination.
It is important for the proper functioning of the electrochemical cell 12 to have electrochemically conductive medium 28 sandwiched tightly between active area 22 of anode cavity 10 and active area 23 to facilitate the interaction of fluid and charge in the cavities. In the past, manufacturers have used a pressure pad 36 to bias the active areas of the anode cavity and the cathode cavity 14 together. Pressure pad 36 is positioned within a frame 40 that ensures the position of pressure pad 36 relative to the active areas 22, 23 of plates 18. The pressure pad 36 is made of rubber with strips of metal to make the pressure pad 36 conductive. However, due to the incompatibility of rubber with fluids used in the electrochemical cell, such as hydrogen and oxygen, manufacturers have been forced to isolate the pressure pad 36 from the fluid in the anode cavity 10 and the cathode cavity 14. A barrier, such as a separator plate 32, is typically used to prevent fluid from anode cavity 10 and cathode cavity 14 from passing to pressure pad 36.
There is generally a pressure difference across the electrochemically conductive medium 28 that arises as a consequence of the different pressures of anode cavity 10 and cathode cavity 14. Due to this difference in pressure, pressure pad 36 must provide an initial preload of pressure in the direction of arrow A to ensure that cathode cavity 14 and anode cavity 10 stay together. Without such a preload, cathode cavity 14 will tend to separate from anode cavity 10. In addition, further preload in the direction of arrow A is required to keep the cavities in close contact. As pressure differentials between the anode cavity 10 and the cathode cavity 14 increase, greater preload in the direction of arrow A of pressure pad 36 is required. This increasing preload puts undue stress on the electrochemically conductive medium 28, which is, in fact, the weakest component of the assembly.
A need therefore exists for an assembly that overcomes the deficiencies of existing pressure pads while still ensuring that the active areas of the anode cavity and the cathode cavity stay together.